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BUG: KCSAN: data-race in __fsnotify_parent / __fsnotify_update_child_dentry_flags

write to 0xffff88811f0f6d80 of 4 bytes by task 20811 on cpu 1:
 __fsnotify_update_child_dentry_flags+0x14c/0x200 fs/notify/fsnotify.c:134
 fsnotify_recalc_mask+0x1ca/0x1e0 fs/notify/mark.c:150
 fsnotify_add_mark_locked+0x79b/0x970 fs/notify/mark.c:668
 fsnotify_add_inode_mark_locked include/linux/fsnotify_backend.h:541 [inline]
 inotify_new_watch fs/notify/inotify/inotify_user.c:592 [inline]
 inotify_update_watch fs/notify/inotify/inotify_user.c:619 [inline]
 __do_sys_inotify_add_watch fs/notify/inotify/inotify_user.c:757 [inline]
 __se_sys_inotify_add_watch+0x55d/0x670 fs/notify/inotify/inotify_user.c:700
 __x64_sys_inotify_add_watch+0x3f/0x50 fs/notify/inotify/inotify_user.c:700
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811f0f6d80 of 4 bytes by task 20774 on cpu 0:
 __fsnotify_parent+0x79/0x470 fs/notify/fsnotify.c:180
 fsnotify_parent include/linux/fsnotify.h:68 [inline]
 fsnotify_file include/linux/fsnotify.h:90 [inline]
 fsnotify_modify include/linux/fsnotify.h:255 [inline]
 do_iter_write+0x426/0x4b0 fs/read_write.c:1022
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1059
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1595 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1587
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20774 Comm: syz-executor.5 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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